I'm not too sure whether or not Queezle died. Her dying always seemed odd to me, though. Let's think about the night of Queezle's "Death":
-There wasn't much sign of a struggle
-The only demons who had been killed by the Golem so-far were ones that tried to be heroic and charged at the Golem to fight it.
-Queezle was scared and had just been told to run away if she did find the Golem. So, it seems unlikely that she would have tried attacking the Golem.
-Golem's aren't very perceptive. They have a hard time finding anything that isn't directly attacking them.
- It took getting hit by a statue to make the Golem aware of Bartimaeus' presence.
- When the Golem attacked Sholto Pinn's shop, it only noticed the Foliot there because it tried to attack the Golem head-on
- Queezle was last scene transformed into a small animal that was hiding under a statue
- It was a dark and rainy night, making it hard for anyone to see anything
-So, based on THIS ^, the Golem would have no chance of spotting Queezle to kill her unless she did something to draw it's attention. And again, I think its much more likely that Queezle would have hid or ran away rather than fighting the Golem.
-Golem's are huge and heavy. The Golem would not have been able to sneak up on Queezle (not that the Golem cared about stealth at all). Queezle would definitely heard the Golem's crashing footsteps or noticed it in someway long before the Golem noticed her.
-Her "Death" happen way too quickly. Bartimaeus and practically Just turned around when he herd Queezle scream. Bartimaeus was already close by and quickly returned to where he last saw Queezle in a matter of seconds. There's no way Queezle could have died so quickly, I believe.
-The fact that no one has seen Queezle since her alleged death doesn't prove anything. The reason no one has seen Queezle is because everyone believes she is dead, so no magicians are trying to summon her.
Theory Time
+Queezle 'faked' her death
-The rumors about the Golem were that anyone who tried to fight it disappeared and was presumed dead. Queezle used this to her advantage.
-When Queezle saw the Golem, she just screamed and, taking Bartimaeus' advice, ran away/hid.
*Whether she planned her disappearance or was just genuinely afraid, or both, is unknown.
-Bartimaeus couldn't find any trace of Queezle due to:
- It was dark and raining = Very poor visibility
- Queezle was hiding or ran so far away that Bartimaeus couldn't find her
- The Golem's essence-draining powers destroyed any trace of Queezle's essence. And/or the Golem's "darkness" blotted out and trails of essence that Queezle had left.
- Bartimaeus kind of quickly thought that Queezle was dead before really doing a thorough search to find her. Bartimaeus was also distracted by his vengeful anger at Queezle's supposed death and by his hunt for the Golem. This could have made Bartimaeus overlook or miss any signs that Queezle was still alive.
-Everyone assumed Queezle was dead, so no tried to summon her or look for her.
-Being a sensible demon, Queezle took this opportunity for freedom and continued to pretend to be dead.